1. Field of the Invention
The present invention relates to an array-like flat lighting source, and more particularly to a light source with an array of field emitter elements.
2. Description of the Related Art
Carbon nanotube, discovered in 1991, has a superior field emission characteristic than traditional field emitters employing tungsten. Cathode material made of carbon nanotubes have been utilized to fabricate carbon nanotube field emission elements and carbon nanotube field emission displays. If the emission efficiency of the carbon nanotube field emission element can be improved up to 80-100 lm/W, it would become commonly used instead of the fluorescent lamp. FIG. 1 is a schematic cross-sectional view of a conventional flat lighting source employing carbon nanotube field emitters, which includes: a cathode substrate 100; an anode substrate 600 stacked over the cathode substrate 100; a spacer 500 disposed between the cathode substrate 100 and anode substrate 600 to maintain a certain vertical distance and vacuum there between. The cathode substrate 100 is a glass substrate, and a cathode electrode layer 200 is formed thereon. A catalyst layer 300 is formed on the cathode electrode layer 200 to facilitate the growth of the carbon nanotubes. Several carbon nanotubes 400 are formed on the catalyst layer 300 to serve as the cathode field emitters. The anode substrate 600 is a glass substrate, and an anode electrode layer of indium tin oxide (ITO) 700 is formed under the anode substrate 600. A fluorescence layer 800 is formed under the anode electrode layer of indium tin oxide 700. The carbon nanotubes 400 inject electrons under attraction of a voltage of the anode electrode layer of ITO 700, and impinge upon the fluorescence layer 800 to excite the fluorescence layer 800 to emit light passing through the anode substrate 600 to form a flat lighting source.
The above flat lighting source employing the carbon nanotubes as the field emitters has several disadvantages. The carbon nanotubes surrounding the periphery of the electron-emitting area have an edge effect, which makes the peripheral brightness of the fluorescence layer 800 larger than its central brightness, and causes uneven brightness of the above flat lighting source. The illumination characteristic of the flat lighting source is lowered. Moreover, the carbon nanotube 400 is made by arc discharge or laser ablation. However, the above two methods are not suitable for low cost manufacture of the carbon nanocarbon tubes. It is also difficult to control the structure of the carbon nanotubes and is thus difficult to produce a large flat lighting source.
Accordingly, it is an intention to provide an improved flat lighting source with field emission characteristic, which can overcome the above drawbacks.